Enterohemorrhagic Escherichia coli infection in Japan as of April 2014

Enterohemorrhagic Escherichia coli (EHEC) infection is a category III notifiable infectious disease under the Law Concerning the Prevention of Infectious Diseases and Medical Care for Patients of Infections (Infectious Diseases Control Law). All cases must be notified by the physician who makes the diagnosis (http://www.niid.go.jp/niid/en/iasr-sp/2251-related-articles/related-articles-399/3534-de3991.html). If an EHEC infection is notified as food poisoning by the physician or judged as such by the director of the health center, the local government investigates the incident and submits a report to the Ministry of Health, Labour and Welfare (MHLW) in compliance with the Food Sanitation Law.

Prefectural and municipal public health institutes (PHIs) conduct isolation of EHEC, serotyping, and toxin [vero-/Shigatoxin: (VT)/(Stx)] typing and report the result to the National Epidemiological Surveillance of Infectious Diseases (NESID) system (see p. 119 of this issue). When necessary, the Department of Bacteriology I, National Institute of Infectious Diseases (NIID), conducts confirmatory tests for sero- and toxin-typing and also conducts multiple-locus variable-number tandem repeat analysis (MLVA), pulsed-field gel electrophoresis (PFGE) and other molecular epidemiological analysis to analyze outbreaks (including sporadic cases part of diffuse outbreaks). These results are informed back to PHIs and made available through the National Epidemiological Surveillance of Foodborne Disease (NESFD) system (see p. 128 of this issue).

Cases notified under NESID: During January to December 2013, a total 4,046 EHEC infections, composed of 2,624 symptomatic and 1,422 asymptomatic (detected during active surveillance of outbreaks or routine stool testing of food preparation staff) cases, were reported (Table 1). The number of symptomatic infections remained stable from 2009 to 2012 (2,602, 2,719, 2,659 and 2,363, respectively). As in previous years, a large peak occurred in summer (Fig. 1). Reported number of cases (including asymptomatic cases) was the highest in Tokyo (382), followed by Fukuoka (271), Kanagawa (218), Aichi (211), and Hokkaido (207). Incidence (cases per 100,000 populations) was the highest in Miyazaki Prefecture (8.35) followed by Saga Prefecture (8.19) and Toyama Prefecture (7.95) (Fig. 2, left). Among those 0-4 years of age, more cases were reported from Miyazaki, Nagasaki and Shimane Prefectures (Fig. 2, right). The young (<30 years of age) and the elderly (≥60 years of age) had a greater proportion of reported cases that were symptomatic relative to those in their 30’s, 40’s and 50’s (Fig. 3).

Hemolytic uremic syndrome (HUS): A total of 87 hemolytic uremic syndrome (HUS) cases (3.3% of symptomatic cases), were reported in 2013 (see p. 130 of this issue). EHEC was isolated from 55 cases, among which 48 were O157, three were O26, and one each of O76, O111, O121 and O165. Among the 55 isolates, 54 were positive for VT2 or VT1 & 2 (98%). One isolate was unknown for VT type. Four fatal cases were reported, among which one had HUS complication (5 years of age) and the others were elderly (one in her 70’s and two in their 90’s).

EHEC isolated by PHIs: In 2013, number of EHEC isolated by PHIs was 2,086 (see p. 119 of this issue), which was far less than the reported number of 4,046 EHEC cases (Table 1). This discrepancy is due to the current situation where clinical or commercial laboratories do not always send specimens to PHIs. The most frequent O-serogroup was O157 (52%), followed by O26 (25%) and O111 (7.2%). Among O157 isolates, those positive for both VT1 and VT2 genes were predominant (63%) as in previous years. Of the O26 isolates, 95.7% were positive only for VT1 and 78.1% of O111 were positive for both VT1 and VT2. Signs and symptoms frequent among the O157-isolated symptomatic cases (n=1,044), were abdominal pain (60%), diarrhea (60%), bloody diarrhea (50%), and fever (22%).

Outbreaks: In 2013, PHIs reported to NESID 34 EHEC outbreaks. Outbreaks involving ten or more EHEC-positive cases are shown in Table 2. Several outbreaks were believed to have occurred via human to human transmissions at nursery schools (pp. 123, 124, 126 and 127 of this issue). In 2013, prefectures reported a total of 13 EHEC incidents involving 105 symptomatic patients (cases that were negative for isolation included) in compliance with the Food Sanitation Law (25 incidents and 714 patients in 2011; 16 incidents and 392 patients in 2012) (see p. 120 of this issue). Although epidemiological linkage was not demonstrated, Department of Bacteriology I, NIID reported that EHEC cases showing the same PFGE pattern was isolated from sporadic cases that occurred diffusely and widely (see p. 128 of this issue).

Prevention and measures to be implemented: In response to persistent food poisonings caused by raw beef, MHLW revised the standards of beef marketed for raw consumption and issued the MHLW notice No. 321 in October 2011. Further, upon the detection of EHEC O157 in the inner part of beef liver, MHLW banned marketing of beef liver for raw consumption (notice No. 404 in July 2012) (IASR 34: 123-124, 2013). As a consequence, the incidence of O157 cases related to consumption of raw beef or raw beef liver decreased considerably in one year from 2011 and that level has been maintained through 2013. In response to O157 outbreaks caused by pickled vegetables, MHLW further modified the hygiene standards of pickled vegetables (Shoku-An-Kan-Hatsu 1012 No.1, 12 October 2012). The basics for preventing EHEC infections are to observe the principles of food poisoning prevention and to avoid consumption of raw or undercooked beef (http://www.gov-online.go.jp/useful/article/201005/4.html). Although Japan experienced no large-scale food poisoning events in 2013, food safety measures, including the assurance of personal hygiene of food handlers, should be further strengthened.

Similar to dysentery bacilli, EHEC establishes infection even at minute doses and can spread from person to person rather easily. The year 2013 experienced many EHEC outbreaks in nursery schools (Table 2, pp. 123, 124, 126 and 127 of this issue). Preventing such outbreaks needs appropriate hygienic practice, such as routine hand washing and sanitary use of children’s pools during summer (see “Infection Control Guidelines for Nurseries” revised in 2012). To prevent the spread of EHEC within patients’ families and to the wider community, health centers should provide instructions on prevention to relevant persons.